1. Field of the Invention
The present invention relates to a magnetic head on which a magnetic recording medium slides so as to record and reproduce information, and to a method for manufacturing such a head. In particular, the invention relates to a magnetic head for floppy disk drives that can perform recording and reproduction on a floppy disk, a flexible disk-like magnetic medium, and to a method suitable for manufacturing such a head.
2. Description of the Prior Art
As an example of such a magnetic head, a conventional magnetic head having the structure shown in FIGS. 1-3 will be explained: it performs recording and reproduction to and from a floppy disk by a so-called tunnel erasing method.
FIG. 1 is a perspective view showing the construction of the main body of the magnetic head. In FIG. 1, reference numeral 1 designates a front core assembly. It is integrally constructed by coupling, via a spacer 6, the front core portions of a recording and reproducing magnetic core 2 and an erasing magnetic core 4 for performing the tunnel erasing.
The recording and reproducing core 2 is constructed by joining a T-shaped front core 2a and an I-shaped front core 2b via a recording and reproducing gap 3, and by further joining a back core 15 to the bottom ends of the front cores 2a and 2b. Likewise, the erasing core 4 is constructed by joining a T-shaped front core 4a and an I-shaped front core 4b via erasing gaps 5 and 5', and by further joining a back core 16 to the bottom ends of the front cores 4a and 4b. The front core portions of the recording and reproducing core 2 and erasing core 4 are coupled via the spacer 6 so as to form the front core assembly 1, followed by the bonding of nonmagnetic sliders 7 and 8 to both sides thereof by an adhesion or glass welding process before the back cores 15 and 16 are joined.
The sliders 7 and 8 slide on a magnetic disk along with the cores 2 and 4 so as to stabilize the sliding of the cores 2 and 4 and to protect them. The sliders 7 and 8 are made of ceramics, and have notches 7b and 8b, thus taking block-like shapes having L-like cross sections, respectively, and are joined to opposite sides of the front core assembly 1 at junction surfaces 7a and 8a which are formed as remainders of the notches.
After the sliders are attached, a coil bobbin 9 on which a recording and reproducing coil 10 is wound, and a coil bobbin 12 on which an erasing coil 13 is wound are mounted on the front cores 2a and 4a of the front core assembly 1, respectively. Subsequently, the back cores 15 and 16 which are coupled via a spacer 17 are joined to the ends of legs of the front cores 2a, 2b, 4a and 4b to form a magnetic head main body 18 as shown in FIG. 2.
Then, as shown in FIG. 2, the magnetic head main body 18 is fixed on a support plate 19, and coil ends 10a and 13a of the coils 10 and 13 are connected to a flexible printed board 20 attached to the support plate 19. Thus, a magnetic head 21 is constructed.
The magnetic head 21 thus constructed is mounted on a head carriage in a floppy disk drive by fixing the support plate 19 thereon. Thus, the top surfaces of the front core assembly 1 and sliders 7 and 8 in FIGS. 1 and 2 comprise a disk sliding surface that slides on a disk, thereby performing recording by the tunnel erasing method as shown in FIG. 3.
The tunnel erasing method forms a data track 22 as follows: first, data are recorded by the recording and reproducing gap 3 on the magnetic disk which slides in the direction of the arrow A in FIG. 3; and then, both sides of the data are erased by the erasing gaps 5 and 5'.
Recently, large capacity floppy disk drives have been developed: even floppy disk drives having a capacity above 10 MB (Mega-Bits) have been produced. The large capacity is achieved by increasing the line recording density and track density. Current floppy disk drives having 1-2 MB capacity have a maximum line recording density of 9.7 KBPI, and a track density of 135 TPI. To achieve a capacity above 10 MB, a line recording density and a track density of three to four times are required: a maximum line recording density above 35 KBPI and a track density of 405 TPI are necessary.
To increase the track density, a servo-signal type recording head in conjunction with a servo-signal type disk on which servo-signals have been previously recorded is used in place of the tunnel erasing type magnetic head 21 as shown in FIGS. 1 and 2.
FIG. 4 is a schematic plan view showing the state of recording on a magnetic disk by using the servo-signal method. The track positioning is carried out based on servo-signals 24 previously written on the magnetic disk, and a data track 22 is formed by writing data with a magnetic head which includes a recording and reproducing core 40 having only one recording and reproducing gap 26. Such a servo-signal type recording head is used in a floppy disk drive of a capacity above 200 TPI.
Here, it must be taken into consideration that compatibility between higher level and lower level machines must be maintained in general use of floppy disk drives. For example, a 3.5 inch, 2 MB machine has read/write compatibility with a 1 MB machine so that the reading and writing of 1 MB can be accomplished. Likewise, a 4 MB machine has read/write compatibility with 1 MB and 2 MB machines. These machines share the same track density of 135 TPI so that the read/write compatibility can be maintained. In contrast with this, when the track densities differ from each other, although the reading of the data of lower track density is possible, the writing thereof is impossible. Thus, the compatibility of programs and data is lost.
To meet the requirement for the compatibility between the machines of different track density, a composite type magnetic head is proposed which includes a magnetic core for the tunnel erasing type and a magnetic core for a servo-signal type which are disposed in parallel in the lateral direction of a track. The structure thereof will be described with reference to FIGS. 5 and 6. In these figures, like or corresponding parts to those of FIGS. 1 and 2 are denoted by the same reference numerals, and the explanation thereof is omitted here.
FIG. 5 is an exploded perspective view showing the construction of a magnetic head main body of this type.
A recording and reproducing core 2 and an erasing core 4 of the tunnel erasing type are arranged by a front core assembly 1 and back cores 15 and 16 in a manner similar to those in FIGS. 1 and 2. Both the cores 2 and 4 are arranged, for example, for a 135 TPI track density. They differ from those in FIGS. 1 and 2 in that the coil bobbin 12 of the erasing core 4 is mounted on a back core 16. For this purpose, the back core 16 is elongated and the front core 4a is shaped like the letter L.
Reference numeral 40 denotes a recording and reproducing core of the servo-signal type, which is arranged as a core for a high track density of 405 TPI or 540 TPI, for example. The recording and reproducing core 40 is completed by joining a back core 29 to the bottom ends of a front core assembly 25 which is constituted by coupling an L-shaped front core 25a and a T-shaped front core 25b via a recording and reproducing gap 26. Then, a bobbin 27 on which a coil 28 is wound is mounted on the front core 25b.
In the assembly process of a magnetic head main body 31 shown in FIG. 6, the core assemblies 1 and 25 are joined by adhesion via a spacer 30 made of a nonmagnetic ferrite or ceramic. The spacer 30 is formed as a thin rectangle corresponding to the top portions of the front core assemblies 1 and 25. The spacer 30 may be constructed by sandwiching a magnetic material by nonmagnetic materials. Then, sliders 7 and 8 are attached to both sides of the front core assemblies 1 and 25.
Subsequently, coil bobbins 9 and 27 are mounted on the front cores 2a and 25b, and then, a coil bobbin 12 of a coil 13 is mounted on a back core 16 which has been coupled with a back core 15 via a spacer 17. After that, the back cores 15 and 16 are joined to the front cores 2a, 2b, 4a and 4b, and a back core 29 is joined to the front cores 25a and 25b. Thus, the magnetic head main body 31 of FIG. 6 is constructed.
Then, as shown in FIG. 7, the magnetic head main body 31 is fixed on a support plate 19 made from a stainless steel or beryllium bronze, and coil ends 10a, 13a and 28a of coils 10, 13 and 28 are connected to a flexible printed board 20 attached to the support plate 19. Thus, a magnetic head 35 is constructed.
When the recording or reproduction is carried out on a magnetic disk by using the magnetic head 31, the read/write compatibility between higher and lower level machines becomes possible by correctly selecting either the recording and reproducing core 2 and erasing core 4 of the front core assembly 1, or the recording and reproducing core 40 of the front core assembly 25 in accordance with the track density.
The conventional composite type magnetic head 31, however, has a problem of crosstalk which is induced by magnetic leakage between the front core assemblies 1 and 25, because they are disposed in close vicinity via the spacer 30 as shown in FIGS. 5 and 6.
For example, consider the case where a higher density disk (for example, 405 TPI servo-signal type) is replayed by a higher level floppy disk drive. In this case, the reproduction of the higher density disk is carried out by the recording and reproducing gap 26 of the front core assembly 25. At the same time, however, the recording and reproducing gap 3 of the front core assembly 1 which is provided for a lower density disk (for example, 135 TPI tunnel erasing type) and is placed in close proximity of the front core assembly 25 will reproduce a plurality of tracks of the higher density disk. This will cause the flux through the front core assembly 1 to leak into the front core assembly 25, thereby inducing crosstalk.
The crosstalk thus induced will degrade the reliability of the read data, and presents an important problem in constructing floppy disk drives. In addition, once crosstalk takes place, the core efficiency during the recording or reproduction reduces. This will results in an increase in current to be applied to the coil 28 to carry out sufficient recording, a decrease in the margin of the reproduced signal, or a decrease in resistance against noise, which requires a change of circuitry of the floppy disk drive or the design modification thereof.